Fluctuations and recent variations of Pisgana Glacier (Adamello Group, Central Italian Alps) during late Holocene

Two distinct glacial bodies (both North facing) presently constitute the Pisgana Glacier, in the Adamello Group, Raethian Alps. The western body (Ghiacciaio di Pisgana Occidentale) is a well defined valley glacier with compound accumulation basin, while the eastern one (Ghiacciaio di Pisgana Orientale) is a simple valley glacier. During the Little Ice Age (LIA), the Pisgana Glacier advanced to its maximum Holocene position and fed three distinct lobes reaching the minimum elevation of 2125 m. We evaluated areal and volumetric variations since the LIA through both direct and indirect investigations. Quantitative analysis of glacier variations was carried on by mean of aerial photographs, orthophotographs, and cartographic material (since 1885 AD) while the maximum Holocene extension was reconstructed by means of geomorphological mapping and glacial geological survey. All the data were processed in GIS environment (Arcmap 9.3, Ilwis 3.3). Volume variations expressed in terms of mass balance from Little Ice Age to 2012 were calculated by comparing different Digital Terrain Models (LIA-1983-2006) and by applying empirical formulas largely used in glaciological research (all the other years). A definitely negative trend, reflecting strongly negative mass balance, brought Pisgana Glacier to halve its area from the Little Ice Age maximum extension to 1983 and further accelerated the contraction later on (to 2012). The general negative trend was interrupted by minor phases of expansion that occurred at the start of 1900 and during the ’80s. Volume reduction exceeds 180 millions of m3 from 1850 to 1983 and the loss further increased until 2006. Results obtained are in agreement with the trend recorded by most glaciers of the Alps since the Little Ice Age, reflecting the strong response that glaciers show respect to the ongoing climate warming.